Reducing chlorination

Two variables of primary importance, which are interdependent, are reaction temperature and ch1orine propy1ene ratio. Propylene is typically used ia excess to act as a diluent and heat sink, thus minimising by-products (eqs.2 and 3). Since higher temperatures favor the desired reaction, standard practice generally involves preheat of the reactor feeds to at least 200°C prior to combination. The heat of reaction is then responsible for further increases in the reaction temperature toward 510°C. The chlorine propylene ratio is adjusted so that, for given preheat temperatures, the desired ultimate reaction temperature is maintained. For example, at a chlorine propylene molar ratio of 0.315, feed temperatures of 200°C (propylene) and 50°C (chlorine) produce an ultimate reaction temperature of approximately 500°C (10). Increases in preheat temperature toward the ultimate reactor temperature, eg, in attempts to decrease yield of equation 1, must be compensated for in reduced chlorine propylene ratio, which reduces the fraction of propylene converted and, thus aHyl chloride quantity produced. A suitable economic optimum combination of preheat temperature and chlorine propylene ratio can be readily deterrnined for individual cases. 

Intravenous administration of methylene blue may be an efifective method for reducing chlorine dioxide- or chlorite-induced increases in methemoglobin. However, this treatment is not effective in G6PD-deficient individuals. 

Arsine is a strong reducing agent, reducing many oxidizing agents, i.e, reduces chlorine to hydrogen chloride ... 

Irreversible oxidation peaks of 5u, PhMgCl and n-HexMgCl recorded at a Pt electrode in THF containing 0.1 M LiBr were fonnd in the same potential range (—2.5 to — 1.5 V vs. Ag+/Ag) as for the irreversible rednction peak of the Cl-terminated Si(lll) surface (—2.5 V). This result evidently shows that 5 can reduce chlorine bonds on the surface, and thus a SET step participates in the alkylation, as included in the mechanism proposed. ... 

Nitrite reductase and sulfite reductase are enzymes found in choroplasts and in prokaryotes that reduce nitrite to ammonia and sulfite to sulfide (Scott et al., 1978). Sulfite reductase also catalyzes reduction of nitrite at a lower rate. Both enzymes contain a siroheme prosthetic group linked to an iron-sulfur cluster. In siroheme, the porphyrinoid moiety is present in the more reduced chlorin form. Because NO lies between nitrite and ammonia in oxidation state, it is a potential intermediate. 

The Fuel Cell (or Electricity Producer). A fuel cell is shown schematically in Fig. 7.5. Instead of pushing the reactions at the electrodes to go against their spontaneous tendency, the fuel cell consumes chemicals (their fuels), and the overall result of the reactions at its two electrodes is the consequence of allowing the reaction in the cell to occur spontaneously. As can be seen from the figure, the electrons produced from the oxidation of the lithium fuel at the one electrode pass out of the cell and travel on through a load (which could be an electric motor) and then pass on to reduce chlorine to chloride at the second electrode (Fig. 7.5). 

Sulphur Dioxide as a Reducing Agent.—When treated in a current of sulphur dioxide, nitrates are reduced, with formation of nitrous gases and sulphates chlorates likewise are reduced, chlorine peroxide being obtained below 60° C., whilst above this temperature the volatile products are sulphur trioxide and chlorine. 

Hydrogen telluride is very sensitive towards the halogen elements. It not only readily reduces chlorine, bromine and iodine to the corresponding hydracids with simultaneous liberation of tellurium (which in the case of chlorine can further pass easily into the tetrachloride), but it also reduces solutions of such salts as ferric chloride and mercuric chloride to the lower chlorides, tellurium being precipitated. It also reduces tellurium chlorides, the only products being hydrogen chloride and tellurium. 

Of the cyclobutene derivatives 76-87 all except 87 undergo clean ROMP. The polymer of 87, obtained in low yield using WClg/Me4Sn as catalyst, is a black insoluble powder of reduced chlorine content, caused by loss of HC1 and development of conjugation335. 

The amount of cathodically reduced chlorine depends on the distance between the electrodes and rate of flow of the brine through the electrolyzer (i. e. on the intensity of stirring of the electrolyte). 

More economical than the above mentioned method are processes in which the chlorine dioxide is absorbed in a solution of sodium hydroxide in the presence of a suitable mild reducing agent, which reduces chlorine dioxide to chlorite only. This reaction proceeds according to the equation ... 

During the war I. G. Farben made experiments to reduce chlorine dioxide by zinc dust dispersed in water ... 

Chlorine and other oxidants are removed using activated carbon by an oxidation/reduction reaction. Chlorine oxidizes the carbon while the chlorine is being reduced. Chlorine ends up forming hydrochloric acid via equation 8.1. 

In a newer steam-based process, vacuum is used, which, by matching the vapor pressure of the hot brine, causes bromine to be stripped out without the need for steam to heat the brine. Claimed benefits are increased plant capacity, reduced chlorine loss, less lime needed to treat the spent brine, lower plant maintenance costs, and decreased atmospheric emissions.44,45... 

Yonkos, L. T. Fisher, D. J. Burton, D. T. Whitekettle, W. K. Petrille, J. C. Effectiveness of the Sulfur(IV) Compound, Sodium Bisulfite, in Reducing Chlorine, Chlorine Dioxide, and Chlorite Toxicity to Daphnia Magna in Well Water and Pond Water, Environ. Toxicol. Chem. 2001, 20, 530-536. 

Wang, J., Zhang, L., Walther, S.M. (2004). Administration of aerosolized terbutaline and budesonide reduces chlorine gas-induced acute lung injury. J. Trauma 56 850-62. 

At present, granular activated carbon (GAC) or sulfur dioxide are known to chemically reduce chlorine dioxide and chlorite ion (but not chlorate ion) to the innocuous chloride ion. 

Ascorbic acid is reasonably stable in a dry state with a shelf life of about 1-3 yr (23). However, it rapidly oxidizes in solution. A 1% solution may remain at approx 80% potency after 10 d. A 0.02% solution will degrade to 0% within 3 d. Ascorbic acid is also currently available in tablet form for dechlorination applications. Release of ascorbic acid-containing waters under some conditions may reduce the pH of the receiving streams. Use of vitamin C is reported to have other potential benefits as it is an essential vitamin for healthy fish (23). Also, it can easily strip manganese oxide stains from reservoir surfaces and thereby promote better disinfection (once the vitamin C is exhausted). Vitamin C (ascorbic acid) is NSF certified, allowing it to be used in drinking water treatment to remove or reduce chlorine levels. 

Use Reduces chlorinated effluent discharge levels in pulp mills. 

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